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The properties of the young stellar populations in powerful radio galaxies at low and intermediate redshift | | J. Holt
; C. N. Tadhunter
; R. M. Gonzalez Delgado
; K. J. Inskip
; J. Rodriguez
; B. H. C. Emonts
; R. Morganti
; K. A. Will
; | | Date: |
20 Aug 2007 | | Abstract: | Abridged. We present high-quality optical spectra for 12 powerful radio
sources at low and intermediate redshifts (z < 0.7) that show evidence for a
substantial UV excess. These data were taken using the WHT and VLT to determine
the detailed properties of the young stellar populations (YSPs) in the host
galaxies as part of a larger project to investigate evolutionary scenarios for
the AGN host galaxies. The results of our spectral synthesis model fits to the
spectra highlight the importance of taking into account AGN-related components
(emission lines, nebular continuum, scattered light) and reddening of the
stellar populations in studies of this type. It is also clear that careful
examination of the fits to the spectra, as well consideration of auxilary
polarimetric and imaging data, are required to avoid degeneracies in the model
solutions. In 3/12 sources in our sample we find broad permitted line
components, and a combination of AGN-related continuum components and an old
(12.5 Gyr) stellar population provides an adequate fit to the data. In the
remaining 9 sources we find strong evidence for YSPs. In contrast to some
recent studies that suggest relatively old post-starburst ages for the YSPs in
radio galaxies (0.3-2.5 Gyr), we deduce a wide range of ages for the YSPs in
our sample objects (0.02-1.5 Gyr), with ~50% of the sample showing evidence for
young YSP ages (<~0.1 Gyr) in their nuclear regions. The nuclear YSPs are often
significantly reddened (0.2 < E(B-V) < 1.4) and make up a substantial fraction
(~1-35%) of the total stellar mass in the regions sampled by the spectroscopic
slits. Moreover, in all the cases in which we have sufficient spatial
resolution we find that the UV excess is extended across the full measureable
extent of the galaxy (typically 5-30 kpc), suggesting galaxy-wide starbursts. | | Source: | arXiv, 0708.2605 | | Services: | Forum | Review | PDF | Favorites | |
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